Tile calculator: how many tiles do I need?

How many tiles do I need for my room?

This tile calculator starts from the area to cover, the tile size and the grout joint width. It shows the number of tiles per square foot (or per m²), the tiles to lay with a waste allowance that suits your layout pattern, the boxes to buy and the area to order. It also estimates tile baseboard, adhesive, grout and, if you enter prices, the budget. It works in feet and inches or in metres and centimetres.

How to use it

1. Pick Floor or Wall, then enter the length and width of Area 1. For an L-shaped room, click Add an area.
2. Under Areas to subtract, add the bathtub, shower tray or fitted cabinets that won't be tiled.
3. Choose the Tile size (or Custom size), the Grout joint width (fractions such as 1/8 work) and the Layout pattern: the suggested Waste allowance fills in by itself.
4. Copy the box contents from the label, as Coverage per box or Tiles per box.
5. Set the baseboard, adhesive and grout, then read the Result block and the step-by-step calculation.

Worked example: a 12 × 10 ft room in 12 × 24 in tile

Straight lay, 1/8 in joints, boxes of 16 ft², one 3 ft door, baseboard pieces 12 in long.

• Area: 12 × 10 = 120 ft².
• One tile plus its joint takes up 12.125 × 24.125 in, so 144 ÷ 292.52 = 0.49 tiles per ft².
• Without waste: 120 × 0.4923 = 59.07 tiles.
• 10% waste for a straight lay: 59.07 × 1.1 = 64.98, rounded up to 65 tiles.
• A 16 ft² box holds 16 ÷ 2 = 8 tiles: 65 ÷ 8 = 8.13, so 9 boxes, 144 ft² to order and 7 spare tiles.
• Baseboard: 2 × (12 + 10) = 44 ft, minus 3 ft of door = 41 ft, plus 10% = 45.1 ft, so 46 pieces.
• Adhesive at 1 lb/ft²: 120 lb, so 3 bags of 50 lb.
• Grout with 3/8 in deep joints: 0.2381 kg/m², which is 0.0488 lb/ft², so 5.85 lb for the room: one 25 lb bag.

The same tool in metric: a 3.2 × 2.5 m bathroom (8 m²) in 60 × 60 cm tile with 3 mm joints gives 2.75 tiles per m², 22.00 tiles without waste, then 15% waste (10% straight lay plus 5% for large format), so 26 tiles. Boxes of 1.44 m² hold 4 tiles: 7 boxes, 10.08 m². With a Diagonal layout the waste goes to 20% and you need 27 tiles. Subtract a 1.2 × 0.9 m shower tray and it drops to 22 tiles in 6 boxes.

The grout formula explained

Grout follows the formula used by grout makers: (L + W) ÷ (L × W) × joint width × joint depth × density, with all sizes in millimetres. The first part is the length of joint per mm² of tiling, the width and depth (the tile thickness) give the joint cross-section, and a density of 1.6 turns the volume into kilograms. For the 60 × 60 cm tile above, 9 mm thick: (600 + 600) ÷ (600 × 600) × 3 × 9 × 1.6 = 0.144 kg/m². Small tiles use far more grout, because there are more joints per square foot.

Tips before you buy

• Check that every box shows the same lot or shade number and keep a few tiles for repairs.
• Stores in the US usually price tile per square foot but sell full boxes only: the Area to order is what you pay for.

Frequently asked questions

How do I work out tiles per square foot?

Divide 144 by the area of one tile plus its joint, in square inches. A 12 × 12 in tile with 1/8 in joints: 144 ÷ (12.125 × 12.125) = 0.98 tiles per ft².

How much extra tile should I buy?

5 to 10% for a straight or brick-bond layout, 15% for diagonal, and about 5% more for large-format tile. The tool suggests these figures; you can enter your own.

Should I subtract doors and windows on a wall?

Yes: add them under Areas to subtract with their width and height, like a niche.

Why does the tool always round up?

You can't buy half a tile or half a box, so every count is rounded up, which leaves a few spare tiles.